1. Field of the Invention
This invention pertains to the field of electronic security systems that detect unwanted intrusions into secured areas and sound an audible alarm in response thereto. More particularly, the invention pertains to a method of differentiating between a high degree of intrusion or threat such as a shock or a low intensity degree of intrusion or insubstantial threat, received by the protected structure or object, and executing an appropriate alarm as well as preventing nonphysical, random energy inputs from tripping the security alarm.
2. Description of the Prior Art
Electronic security systems have been used for some years and their popularity increases as the national crime rate continues to climb. Most such systems, especially those used for protection of automobiles, include a controller, a series of intrusion sensors for detecting attempted intrusions through doors, hood, and windows, an alarm for activation upon receipt of a signal or signals from the sensors indicating an attempted unwanted entry into the vehicle, and a power source, normally the vehicle battery, to power the system and sound the alarm. Other components are often included such as automatic resetting circuits and shut-down devices for use when the alarm needs to be deactivated. These systems may be original equipment on new vehicles or retrofitted on existing vehicles.
The security systems may be effected by a nonphysical signals, or electrical surges commonplace in the automobile circuitry. The intended arming and disarming of an alarm system is usually performed by sending a digitally coded signal, by a hand-held transmitter operated by one or more push buttons. In addition, other such systems may be armed by mere passage of time following the driver's act of turning off the engine and exiting the vehicle with the doors and windows closed and after a short time interval such as thirty (30) seconds. Thereafter the system may be disarmed by a hand-held transmitter or by a delay circuit that activates the alarm if the system is not disarmed by the driver upon entry into the vehicle. The first type of arming is known as "active arming" while the latter is known as "passive arming".
Upon detection of an attempted intrusion into the vehicle by one of the sensors, the alarm is activated for a period of time, for instance thirty (30) seconds to one (1) minute, and then, if the alarm has not been disarmed by the remote transmitter or by the manipulation of a "kill" switch, mounted interior the vehicle, usually in a hidden area therein, the alarm response terminates or times-out and the security system is once again reset to monitor the sensors and triggers.
One form of such a sensor is called a "shock" sensor. The shock sensor technology of this invention is discussed in Applicants' patent application Ser. No. 08/112,940. However, a number of other sensors may be employed within the alarm system of this invention. This invention includes, but is not limited to, the application of shock sensors, motion sensors, field disturbance sensors, sound discriminators, ultrasonic sensors, current sensors and other sensors which sense disturbance or threat applied to or about an area and generate an electrical signal in response thereto. An incoming threat to the protected area such a vehicle includes threats such as physical impact, activity in or about the vehicle, breach of the vehicle electric system, the sound of breaking glass, or other activity results in the sensing of the activity and generation of an electrical signal which is then interpreted by the alarm controller to generate an alarm response.
Certain problems exist with conventional security systems that render their usage less than desirable under certain circumstances. For example, a shopping cart inadvertently bumped against the vehicle will usually cause a full alarm response. While the alarm is certainly necessary to alert the owner, inadvertent tripping of the alarm is annoying and could result in either the owner becoming frustrated, and thereafter not activating the alarm, or convincing the shopper or other car owners that such a loud, annoying alarm is not what they want in their vehicles.
In other situations, certain transient electric fields can invade the circuitry of the alarm system and generate enough of a signal to trip the alarm even in the absence of intrusion to the secured area. When a warn signal is generated by the alarm, it flashes the running lights which generates electrical surges or transients. These transients may generate electrical signals which may feed into the alarm circuitry where they are amplified and trip full alarm. In other situations, such as where a cellular telephone is used about the vehicle, the initial surge of the wireless transmission signal may be sufficient to generate an actuation level signal resulting in the activation of the alarm. Still further, in isolated cases, such as where a police car parks behind a protected area and the officer "keys" the microphone on his radio, the surge from his transmitter could interact with the anti-theft system induction coil and produce a false alarm.
Still further, there are instances where a disturbance continues unabated after the initial activation of the alarm sequence. For instance, a vehicle parked next to a train station may receive an alarm input generated by a passing train. The alarm will commence and terminate after running its course, yet often the train has not passed completely by the vehicle. In the prior art, the alarm will sound again because of the continuous input of energy from the train. This can be of annoyance to others in the area.
Crowded parking lots are prime areas for car theft. In these cases, dissatisfaction with the anti-theft system may cause the owner to cease arming the system thus rendering the vehicle subject to theft. This condition, if not corrected, may cause other vehicle owners to cease purchasing such security systems for fear of annoying others and thereby undermine the desirability for and effectiveness of anti-theft devices.
What is needed to circumvent the drawbacks heretofore described is (1) a vehicle security system capable of differentiation between a light, generally non-threatening intrusion event and a stronger, usually security-threatening intrusion event to the vehicle and output a pulse to the alarm circuit appropriate to the degree of intrusion about the secured area, and (2) a vehicle security system that will discriminate between the non-threatening events and block them or otherwise divert the signals they produce so that an alarm is not generated.